EFFECTS OF IRON STRESS ON CHROMATIC ADAPTATION BY NATURAL PHYTOPLANKTON COMMUNITIES IN THE SOUTHERN-OCEAN

Effects of iron stress on chromatic adaptation were studied in natural phytoplankton communities collected in the Pacific region of the Sout hern Ocean. Iron enrichment experiments (48 to 72 h) were performed, i ncubating plankton communities under white, green and blue light respe ctively, with and without addition of 2 nM Fe. Pigment ratios were aff ected by iron addition only to a minor extent. The pigment composition as dictated by the light conditions was similar for both the iron-enr iched and the unamended bottles. Upon iron addition, phytoplankton aut o-fluorescence, as estimated by flow cytometry, decreased markedly, in dicating iron stress of the endemic phytoplankton community. It was co ncluded that iron did not control chromatic adaptation via the pigment composition, but exerted a clear effect on the efficiency of electron transfer.